1. Field of Invention
This invention relates generally to improvements in methods and apparatuses for dynamic information storage or retrieval, and more specifically to improvements in circuits for use in mass data storage devices to measure the slew rate of signals at motor driver transistors to facilitating testing of the circuitry of the mass data storage device.
2. Relevant Background
Mass data storage devices include tape drives, as well as hard disk drives that have one or more spinning magnetic disks or platters onto which data is recorded for storage and subsequent retrieval. Hard disk drives may be used in many applications, including personal computers, set top boxes, video and television applications, audio applications, or some mix thereof. Applications for hard disk drives still being developed, and are expected to further increase in the future.
Mass data storage devices may also include optical disks in which the optical properties of a spinning disk are locally varied to provide a reflectivity gradient that can be detected by a laser transducer head, or the like. Optical disks may be used, for example, to contain data, music, or other information.
Such mass data storage devices typically have a polyphase motor, usually a three-phase motor, that has a spindle that rotates the memory media. The motor is typically controlled by a DMOS power H-bridge circuit to which drive voltages are commutatively applied to drive currents through the motor coils in a known manner. Typically the H-bridge has a number of xe2x80x9chigh-sidexe2x80x9d and xe2x80x9clow-sidexe2x80x9d driver transistors that respectively connect the commutatively selected coil combinations to a power source and ground. More specifically, the coils are typically connected in a xe2x80x9cYxe2x80x9d configuration, with a common end of each coil interconnected, and with the other ends connected between the respective high and low DMOS devices in each H-bridge power transistor pair. Thus, the unconnected ends of the motor coils are typically connected in a known sequence among a power source and ground, with the third phase floating or connected to a tri-state impedance.
During commutation, however, to ensure that transistors that connect the selected coil to the power source and ground in the same phase are not simultaneously conducting (an undesirable condition known as shoot-through), the driving voltages are usually slewed at a predetermined rate. This slew rate may be programmable in some applications, and may be factory set in others. In any event, it is important to know the slew rate in testing the device to ensure that the motor will properly perform. Since the DMOS devices of the power transistor H-bridge are generally large devices, a large capacitance may be associated with the gate elements of the DMOS devices. Such large capacitances also may affect the slew rate, and may cause the motor to not properly perform, which is another reason that the slew rate should be measured or tested before the motor is put into service.
However, in a Spindle/VCM driver IC with on chip power DMOS devices, a large amount of test time may be required to measure the charge and discharge capabilities of, the DMOS predrivers. Since the predriver outputs are not brought out to externally accessible pins, extra hardware may be required for the test board to be enabled to provide a suitable measurement method. It also takes a lot of time to measure the analog currents and voltages that appear between the H-bridge power devices and the predriver circuitry.
What is needed, therefore, is a method and apparatus for easily measuring the voltages and currents between the H-bridge power devices and the predriver circuitry, and more particularly to a method and apparatus that simplifies the measurement of the slew rate of the driving voltages in devices of the type to which the invention pertains.
In light of the above, therefore, it is an object of the invention to provide a digital circuit to measure the rise and fall times of predriver signals of a spindle driver circuit.
It is another object of the invention to provide a circuit that develops a timing window in which the rise and fall times are determined.
It is another object of the invention to provide a circuit that can reduce test time, resulting in the advantage that more flexibility can be achieved for spindle pre-driver testing.
It is another object of the invention to provide a circuit that includes variations in the power DMOS gate capacitances.
It is another object of the invention to provide a circuit that enables a faster slew rate measurement.
These and other objects, features and advantages of the invention will be apparent to those skilled in the art from the following detailed description of the invention, when read in conjunction with the accompanying drawings and appended claims.
This invention uses certain signals from the Spindle Predrivers that are indicative of the beginning of charge/discharge as well as the end. These signals are then initially processed to provide a timing window which determines the predrivers rise and fail times.
The approach followed by the circuit a method of the invention requires capturing of digital output through a MUX and measuring the timing of those signals to provide spindle pre-drivers slew rates. This minimizes any hardware changes and reduces test time significantly when the predriver outputs are not accessible, for example, because of integrated power DMOS in the IC.
Using the circuit of the invention for measuring digital output parameters, and more particularly, of the gate charge and discharge rates, will cut down the test time significantly. This circuit provides a digital signal whose timing provides the equivalent current and voltage information of the predrivers. By measuring the timing of digital signals, which may be brought out through a digital multiplexer pin, which in most cases exists for other purposes, test time can be significantly reduced, and much more flexibility can be achieved for spindle pre-driver testing.
In contrast to the presently employed analog techniques where as the gate charge and discharge currents are measured via an analog multiplexer pin with external hardware modification, the circuit and method of the invention eliminates the need for these, and a faster measurement can be made. Moreover, the invention enables the true slew rate for the gates to be determined, including variations in the gate capacitance of the power DMOS gates. Also, the invention, in contrast to previously employed analog measurement techniques, is free of variations in the gate capacitance of integrated power DMOS devices, which have wide process variations.
According to a broad aspect of the invention, a circuit is presented for providing digital signals indicative of slew rates of motor driver signals. The circuit includes a multiplexer connected to direct at least some of the driver signals to a multiplexer output port and a digital comparison circuit for receiving the driver signals on the multiplexer output port and for producing a digital output having signal changes in dependence upon rise and fall times of the driver signals.
According to another broad aspect of the invention, a circuit combination is presented for providing digital signals indicative of slew rates of drive signals provided to H-bridge power drive transistors of a motor of a mass data storage device. The circuit combination includes a plurality of predriver circuits producing predrive signals according to a commutation sequence for connection to respective the power drive transistors. A multiplexer is connected to selectively direct at least some of the drive signals to a multiplexer output port, and a digital comparison circuit for receiving the at least some drive signals from the multiplexer output port and for producing a digital output having signal changes in dependence upon rise and fall times of the predriver output signals.
According to yet another broad aspect of the invention, a circuit combination is presented for providing digital signals indicative of slew rates of predrive signals in a motor driver circuit. The circuit combination includes an integrated circuit chip which has DMOS power driver transistors connected in an H-bridge configuration having a plurality of high-side drivers and a plurality of low-side drivers for providing drive voltages for connection to respective phases of a polyphase motor, a plurality of predriver circuits producing predrive signals according to a commutation sequence connected to gates of respective the DMOS power drive transistors, and a multiplexer connected to selectively direct at least some of the predrive signals to an externally accessible port. The circuit also has a digital comparison circuit for receiving the at least some predrive signals and for producing a digital output having a signal state change time in dependence upon rise and fall times of the predrive signals.
According to still yet another broad aspect.of the invention, a method is presented for providing digital signals indicative of slew rates of motor driver signals. The method includes connecting a multiplexer to direct at least some of the driver signals to a multiplexer output port, and receiving the driver signals on the multiplexer output port and producing a digital output having signal changes in dependence upon rise and fall times of the driver signals.
According to still another broad aspect of the invention, a method is presented for providing digital signals indicative of slew rates of predrive signals in a motor driver circuit. The method include proving an integrated circuit chip including DMOS power driver transistors connected in an H-bridge configuration having a plurality of high-side drivers and a plurality of low-side drivers for providing drive voltages for connection to respective phases of a polyphase motor, a plurality of predriver circuits producing predrive signals according to a commutation sequence connected to gates of respective the DMOS power drive transistors, and a multiplexer connected to selectively direct at least some of the predrive signals to an externally accessible port. The method also includes providing a digital comparison circuit for receiving the at least some predrive signals and for producing a digital output having a signal state change time in dependence upon rise and fall times of the predrive signals.